Resistance welding metals of different thicknesses



Feb. 2l, 1950 J. HEUscHKEL 2,498,492

RESISTANCE WELDING METAL OF DIFFERENT THICKNESSES Filed July 21, 1949 5 Sheets-Sheet l ATTORNEY w/////////7/ R m k 2 m \aa, n \v n m 5. 6 ,M W, n Wm Q P, 7 J H new, Lut W W\ /MIM .K|| f, mw W w- J/// f 7 7 y f 4 e an 5 f w .7.. P w w my mi 4%/ E f@ @3 Feb. Z1, 1950" .1. HEuscHKl-:L

RESISTANCE WELDING METAL 0F DIFFERENT THICKNESSES Filed July 2l, 1949 3 Sheets-Sheet 2 Efl- 3 NIMI/d/ INVENTOR JuLlus HEUSCHKEL.

ATTORNEY .y 5., 3 9 w @am www J. HEUscHKEl. 2,498,492

RESISTANCE WELDING METAL OF DIFFERENT THICKNESSES Feb, 21, 1950 I5 Sheets-Sheet S5 Filed July 2l, 1949 ATTORNEY Patented Feb. 21, 1950 UNITED STATES RESISTANCE WELDING METALS F DIFFERENT THICKNESSES Julius Heuschkel, Pittsburgh, la., assigner to Westinghouse lElectric Corporation, East Pittsburgh, Pa., a corporation of yPennsylvania Application July 21, 1949, `Serial No. 105,971

My invention relates to control apparatus and methods and it has particular relation to apparatus and methods for welding materials of different thicknesses. This application is a continuation-in-*part of application Serial No. 69,643, led January 7, 1949, now abandoned, to me, whichis in turn a continuation-in-part of application Serial No. '705,366,1iled October 24, 1946, to Philip M. La Hue .and me. This application also relates to an application, Serial No. 1,523, led January 10, 1948, to -Clarence B. Stadum. The La Hue and Stadum applications are predominantly directed to apparatus which is particularly propitious for practicing the methods to Which the present application is directed.

My invention is particularly applicable to resistance welding systems in which the material to be welded is clamped between welding electrodes, and current is 'transmitted through the material for a predetermined time interval the length of which is dependent on the properties of the material and particularly on its thickness. Experience has demonstrated that, to produce satisfactory welds, the time interval during which Welding current hows should increase as a function of the th-ickness of the material welded. Where materials of diiierent thickness are to be welded, this requirement presents difficulties. It is not practicable to segregate the materials to be Welded in accordance with their thicknesses and to weld the material of each thickness in its turn, resetting the timing with the change in material to be Welded. The segregating operation and the tools which it reouiresare costly in the few situations where it could be carried out. In most situations, the materials to he Welded are not available Yfor segregation. This condition arises for example where a Welder is installed as a component of a. production line, and parts of diierent thickness to be welded arrive from a 'preceding stage in the line.

It is accordingly an object of my invention to provide a method Aof satisfactorily welding materia-ls of different thicknesses which shall lend itself readily to practice ina high speed production line.

A further object of my invention is to provide a method of satisfactorily welding materials of different thicknesses in the practice of Which manual resetting of the welding current time for different thicknesses shall not be required.

Still another object-of my invention is to provide a method of welding materials of different thicknesses without segregating the materials in accordance with their'thicknesses.

A Specific object of my invention is to provide a Amethod of welding steel parts .of different thickmesses without manu-ally resetting the timing of the welding current.

The properties of a weld are determined by a 7 Claims. (Cl. 21S-10) multitude of conditions many of which are 'beyond the :control of the operator. There are, however, :a few Awhicl'lfcim be set by the operator kand which have .an important bearing on its soundness. Of the latter, the principal factors are the pressure applied to the material during theswelding operation, the dimensions .of the welding electrode tips, the magnitude of the welding current transmitted through the material and the time during the welding current flows.

My invention arises .from the realization, as the result of extensive experimental investigation, vthat materials of different thicknesses over a wide range of thicknesses may be welded satisfactorily by varying only the duration of the .flow of Welding current in accordance with the thickness while maintaining lthe pressure exerted by the electrodes, the tip dimensions of the electrodes and the magnitude of the welding current constant. I have found that the welding electrode tipI dimensions and the magnitude of the welding current are each functions only of the welding electrode pressure. The ,pressure required for sound welds determined as a function of a se lected maximum thickness is satisfactory over a wide range of smaller thickness, and with this parameter fixed 'the time duration ofthe welding current which is required for the production vof fa. sound weld is in itself a iunctionof the thickness.

The experiments on which my invention nlts specific aspects is based were conducted principally with low carbon steel (0.15% maximum carbon content) in the hot-rolled or annealed condition. In the remainder of this specification and in the claims, I shall refer to steel of this type as low carbon steel. The principles which I have derived from these experiments are applicable to materials of other types. For low carbon steel, l have found that to achieve a weld of the highest degree of soundness, the smallest electrode force FS which must be applied may be expressed as a function of the thickness of a single sheet as follows:

where FS is in pounds and vt is in inches. Except in rare instances, industry does not demand the highest `deg-ree of soundness; welds which-do not reach this quality are acceptable. The smallest electrode force F in `pounds Which must be applied to produce .an acceptable weld is given by a sphere having a iiat circular end. The spherical portion extends symmetrically about the main axis of the electrode, and the flat tip is, in effect,

a small circle of the sphere cut off by a planev through the sphere perpendicular to the main axis of the electrode. Between the periphery of the iiat circular tip and the surface of the spherical portion above the tip there is a short tapered surface, the taper extending outward from the periphery of the circle to the surface of the sphere. The tapered section in effect is in the form of a truncated cone having the at end and a small circle of the sphere as bases. The angle of taper A is defined as the angle between the horizontal and the tapered surface with the electr'ode in a position such that its longitudinal axis is' vertical. The dimension of the welding electrode tip is a function of F. The flat end diameter d,"the angle of taper A, and the spherical radius R of the electrode tip may be expressed as a function of F as follows:

In these equations d and R are in inches, and A isin degrees.

, The welding current I may be expressed as a function of the force F as follows:

I= (137,000F1/2+ 13,800F-i-285F2/3) lf2 where I is in R. M. S. amperes.

With the electrode force F, fixed, and the electrode tip dimensions and the current determined as a function of the force, the welding time eX- press'ed in terms of cycles N of a 60-cycle welding supply is given in terms of the thickness t as follows:

N =200t+1440t2+5760t3 This relationship may also be written conveniently T=1.6'7..Tl-6J?l12J3 wher-e T is expressed in seconds, that is and J is the total thickness of the material between the welding electrodes, that is The above equations were derived empirically from many experiments conducted with lovv carbon steel. Similar equations may be derived em pirically for other materials. The basic principles of my invention are as applicable to such other materials as they are'to low carbon steel. My invention in its broader aspects extends to any material.

f In the practice of my invention, the electrode force for welding materials over a wide range of thickness is determined from the equation for F' if the materials are of steel, or from an analogous equation if the materials are of other metals. The thickness t selected for calculating F is one-half the thickness of the thickest joint to be welded. Once F is determined, the electrode tip dimensions and the welding current magnitude I may be derived from F. In conducting the welding operation, the electrode tip' dimensions, F and I, are maintained con stant and the duration of the welding current for each weld is varied. Customarily, the weldiifigcurrent isderived from a 60-cycle commercialfsupply. The duration is in such a situation determined from the equation for N. If the supply is not of the Gil-cycle type, a suitable equation for the frequency in question may be derived, or the equation for T may be used.

In certain situations the range of thickness over which a system according to my invention operates can be increased by varying the current I as well as the time (N). Under such circumstances the thickness gauge can be connected to vary the heat control, that is. the current I as well as the time systems in which such variations are available are within the scope of my invention. Under certain circumstances the force F may also be varied, however not at random, Ilout as a specific function of predetermined properties of the material.

My invention is conceived primarily to serve to produce satisfactory welds over a wide range of material thicknesses. However, it has other applications. material welded becomes soft and tends to collapse under the pressure of the welding electrodes. I have found that the extent of the collapse may serve as a criterion of the quality of the weld produced. Sound welds may be produced by observing when the collapse has reached a predetermined point and at this instant discontinuing the ow of welding current. Since the control system in accordance with my invention operates in response to the thickness ofthe material .between the welding electrodes, this system may be utilized to interrupt the welding current when the material between the electrodes has collapsed to the propitious thickness.

The novel features that I consider characteristic of my invention are set forth with partic ularity in the appended claims. My invention itself, however, both as to its organization and its vmethod of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

` Figure 1 is a view partly in side elevation and partly diagrammatic of a welding system for practicing my invention;

Fig. 2 is a view in top elevation of a thickness gauge for practicing my invention;

Fig. 3 is a View in section taken along line III-III of Fig. 2;

Fig. 4 is a partial view in section similar to Fig. 2 and showing the gauge in a diiferent position than it is shown in Fig. 3;

Fig. 5 is a view in section taken along line V--V of Fig. 3; and i Fig.A 6 is a diagrammatic view showing a control circuit for practicing my invention. i

The apparatus shown 'in'Figs l to 6 comprises a welding transformer mounted in a casing i5. In Figs. 1 and 6, the transformer is shown schee matically. It includes a primary l1 and a single or double turn secondary I9. Systems including welding transformers with multiple winding pri-v maries lie within the scope of my invention. The primary I1 is supplied from power busses 2l through a timer 23. Welding electrodes 25 and 2,1 are connected across the secondary i9. The lower electrode 25 is fixed and the upper electrode 27 is mounted in a block 29 which is movable upwardly and downwardly preferably :by operation of a hydraulic system 33. customarily such f3/hydraulic systemcomprises a compressed air supply and the usual solenoid operated inlet and outlet valves. i vIn accordance with the broader aspects of -my invention the block 29 may be During a welding operation, thev electromagnetically or spring operated. The operation may be such for example that the pressure is a predetermined function of thickness, current or other property of the welding system.

A thickness gauge 35 is suspended from a face of the block 29 perpendicular to the -face to which the welding electrode 21 is secured. The thickness gauge is provided with a feeler rod 31 which is held resiliently in its lowermost position in the gauge container 39. When the block 29, the movable electrode 21 and the gauge 3.5 are moved downward, the ieeler rod engages the top of an adjustable screw 4| mounted .on the ilxed electrode support `|3. After the rod 31 has just contacted the screw 4|, the rod is urged upward relative to the gauge container 39- bythe screw as the electrode assembly 21, 29, 39 continues to `move downward. The extent of the upward movement of the rod is determined by the thickness of the material 45 to be welded which is interposed between the electrodes and 21.

The thickness gauge container 39 is in the form of a rectangular parallelepiped. `The body 41 of the container is cast in one piece. Internal bosses 49 are cast integral with one side 5| of the body and centrally with the opposite side :53 and into these bosses screws 55 securing the top 51 and base 5S of the container to the body are inserted. From the `rear wall `5| o the body perforated ears 63 extend; by means of these ears the body is secured to the electrode block 29. rPhe side 53 oi the single boss 49 `is provided with an opening having a rubber grcmmet B5 through which .connecting cables 59, 61, 1| and 13 maybe threaded. From the opposite side 5|, an elongated boss 15 substantially larger than the screw bosses 49 projects centrally. This boss is 'in the form of a hollow cylinder.

Within the body 41 spaced a short distance from the base 5B, a plurality of snap :switches 11, 18 and 81| are mounted with their bodies parallel to the base. The snap switches extend across the width of the body 41 and are mounted therein on a pair of screws 33 which extend from the back wall 6| to the front wall 85 of the body through openings in the snap switches.

This material 45 to be welded is ordinarily of relatively small thickness of the order of hundredths or even thousandths of an inch.v The differences in thickness on which the operation of the gauge 35 depends are, therefore, relatively small. The snap switches 11, 19 and 8| should, therefore, be designed to respond to small differences in pressure or small movements. In the practice of my invention, micro switches manufactured kby the Micro Switch Corporation oi Freeport, Illinois, may be used. A suitable switch is shown on lpage 6 of the Micro Switch Corporation Catalog No. 70.

Each of the snap switches 11, 19 or 8| comprises a pair of iixed contacts 85 and 81 respectively and a movable contact 89 which may he actuated to engage either of the xed contacts. The movable contact 89 is suspended from a spring 9| having a cantilever support from a screw 93 secured -to the base 95 of the switch. The spring is composed of a central elongated strip 81 and a pair of short arms 99 which join in a shoulder to which the movable contact 89 is secured. The short arms 9| of the spring are held in compression by engagement in a V bracket-Uil. Dini/nward pressure oi a spring actuated plunger head .t3 .causes the movable contact .E3 to .engage .the lower fixed contact 85. When this pres-sure is decreased `by a movement of 'the plunger head |03 over a short distance oi the order ci a thousandth or a hundredth of an inch, the movable contact 89 snaps into engagement with the `upper xed contact V81. The plunger of the switch is of composite structure, and comprises a tubular shell |05 having inwardly extending flanges and closed by a button |01. The shell is mounted slidably within an outer shell |09 secured in the cover of the switch. Within the tubular member a rod ||3 flanged intermediate its .ends is slidably mounted. The flange i5 of the rod engages the side wall-o1 the .inner .shell |05. From the projecting `end of the rod a pin |.|1 extends; the pin carries the piunger head |03. The button |01 is resiliently urged away from the cantilever spring 9| by a coil spring H9 which encircles the rod .I |`3 engaging the flange I5 at one end and the inner face of the button at the other. The plunger head |03 may be moved into engagement with the cantilever spring and its pressure on the spring may be increased by pressing downwardly on the button |01.

The position of the button |01 of each switch 11, 179 is determined by -a plurality of adjustable screws |2|, |23 and |25 respectively mounted in a bracket |21. The bracket |21 is in the form of a hoe and comprises a plate |29 from the center of 'one end of which a hollow tubular projection 13| extends. The plate has a length somewhat smaller than the width of the body 41. Its wid-th is equal approxi-mately to half the length of the body.. The bracket |21 is mounted in the container with the projection |3| extending slida-bly into the cylindrical *boss 15, and its outer surface engaging bearings |33 in the boss. Each of the screws |2|, |23, |25 screws into a nut |35 mounted in a hole in the plate |29. The position of the screws may be set by screwing them in or out of the nut |35.

l The screw 23 associated with the central switch 19 screws into a nut centrally disposed in the pate |29 of the bracket |21. This screw is headless and is provided at the top with a hexagonal opening into which a wrench (not shown) may be inserted. The length of the screw is such that it extends lbelow the top v51 of the container 35. The wrench may be inserted through an opening |36 in the top coextensive with the screw. Preferably, the screw ,is preset at the factory to a position such that the corresponding switch button is compressed when the movable welding electrode 21 is in engagement with the fixed welding electrode 25. This `setting is designed for the welding of the thinnest material.

The screws |2| and 4|25 associated with the other switches 11 `and 8| respectively have knurled heads |31 and are screwed into nuts 35 secured in the plate |29 through openings |39 in the top 51.. Each of the screws |31 and |25 is provided with a locking mechanism. The latter comprises a cylindrical shell |4| and a lock nut .|43 having a projection |45. The nut |43 is screwed on each screw to a position near its head |31; the shell 4| is slipped on below the nut. The .assembly vis then screwed into the nut |35 in the plate |29. The outside diameter of the shell |41 is smaller than the diameter of the hole |30 in the top 51. Each screw |2l, |25 is then screwed down to the desired position and locked by screwing the lock nut |43 to a position such that the shell 141| `engages the plate |29.

The bracket l| 21 is held in a downward position, .so that the screws 2| |23 and |25 which it carries `compress the corresponding buttons |91 of the switches 11, 19 and 8| respectively, by heavy helical springs |41 disposed on opposite sides of the boss 15. Each of the springs |41 is secured to a screw |49 extending from the adjacent side wall of the body 41 near the base 59 and to a screw IM extending from the plate |29.

The feeler rod 31 is cylindrical and is dimensioned to slide within the projection |3| of the bracket |21. The rod is provided with a peripheral groove |53 intermediate its ends. Within the groove a relatively heavy circular spring |55 is held. The rod 31 is slipped into the bracket projection |3| to a point at which the circular spring |55 engages the extendingedge of the projection |3I. Further movement of the rod 31 tends `to cause the projection and the bracket to move'` upwardly. As the feeler rod 31 is pressed down on the screw 4I on the xed electrode support 43 by the downward movement of electrode block 29, it moves upwardly relative to the container by the head of the screw 4| and it carries with it the bracket |21. The bracket in turn carries the screws |2I, |23, |25 away from the lbuttons |91. of the switches 11, 19, 8|, causing the latter to snap to different positions from the ones in which they are originally set.

The screws |2|, |23, |25 may be set by trial and error so that only the switch 19 in the center is in the lower position when material 45 of the smallest thickness is to be welded, two of the switches 11 and 19 are in the lower position for materials of an intermediate thickness preselected experimentally and all switches are in the lower position for the thickest material.

In the event that force exceeding the holding force of the circular spring is impressed on the rod 31, the spring is disengaged from its groove by the reactive force exerted by the edge of the bracket projection |3| and may move upwardly. To permit free movement of the rod, an opening |51 is provided in the top 51 of the container. This feature has an important function in the ordinary use of the gauge. Frequently, the operator of a welding machine, in a playful mood or by inadvertence, projects the electrode lever 3| downward in the absence of a material 45 on the lower electrode 25, or in the absence of a lower electrode. Under such circumstances, the feeler rod l31 is urged to move upwardly relative to the container 35 a relatively great distance. If the rod carriedA with it the bracket |21, it would cause the bracket to strike against the top 5| with substantial force, damaging the top or the rod. In the gauge disclosed, the circular spring |55 yields on excessive movement of the feeler rod, the rod moves through 'the top 51 of the container and'I damage is avoided. A

The switches 11, 19 and9| are connected to the timer 2| to control the timing of the welding operation. The connection may be of anyrgeneral type and in general depends on the character of the timer. A typical timingsystem including the switches is shown diagrammatically in Fig. 6. The system includes a pair of ignitrons |59 connected in antiparallel between the power supply busses 2| and the primary l1 of the welding transformer. Firing current is supplied to the ignitrons through a pair of thyratrons |9'|. The anode |63 of each of the thyratrons is connected to an anode |95 of a corresponding ignitron; the cathodes |61 of the thyratrons are connected each tothe corresponding ignitors |99. Each' of the thyr'atrons vis maintained normally non-conductive by a bias impressed between its control electrode |1| and its cathode |61 from a rectifier |13 supplied from the busses 2|. Each thyratron is in its turn rendered conductive by potential derived from the main busses through a phase shifter |15 and a transformer |11. The output circuit of the phase shifter is controlled by a relay |19, the contacts |9| of which are maintained open when the thyratrons |61 are to be non-conductive.

The operation of the system is controlled from a plurality of thyratrons |93, |95, |81 and |89 respectively connected to time its various sequential operations. Each cf these thyratrons comprises an anode |9I, a cathode |93 and a grid |95. The cathodes |93 ofv the thyratrons |83, |85, |81 and |99 lare connected together to an intermediate tap |91 of a secondary section |99 of a transformer energized from the busses 2|.

The first thyratrons |93 control the so-called squeeze time, that is, the time during which the work 45 is compressed between the electrodes 25 and 21 before current iiows. The anode I9| of this thyratron is connected through the exciting coil 29| of a squeeze time relay to the upper terminal of the secondary |99. The control electrode |95 of the thyratron |99 is connected to the lower terminal of the secondary |99' through a capacitor 293, a resistor 295, normally closed contacts 291 of the Welder solenoid relay 299 and a second resistor 2| During the half periods of the power supply during which the anode |9| of the squeeze thyratron |83 is electrically negative relative to the cathode |93, the control electrode |93 is electrically positive and current is conducted to charge the capacitor 293 to a potential such as to maintain the start control electrode electrically negative relative to the cathode. Under such circumstances, the squeeze thyratron |83 remains non-conductive when its anode |9| subsequently becomes positive relative to its cathode. The capacitor is shunted by a voltage divider 2|3.

The second thyratron |81 controls the weld" time, that is, the time during which welding current flows. Its anode |9| is connected to the 11pper terminal of the secondary |99 through the exciting coil 2|5 of the welding relay. Its control electrode i 95 is connected to the lower terminal of the secondary |99 through a capacitor 2|1, a resistor 2|9, normally closed contacts 22| of the squeeze relay and the resistor 2H. This capacitor 2|1 is charged by flow of grid current to a potential such as to maintain the weld thyratron |85 non-conductive. y One of a plurality of shunt networks, each including a voltage divider 223, 225, or 221 may be selectively connected across the capacitor 2|1. The selection of these shunt networks is controlled from the snap switches 11, 19 and 3| respectively of the thickness gauge. With the buttons |91 o f all snap switches 11, 19, 8| compressed and their movable conductors in the lower position and shunting network across the weld time capacitor 2 I1 includes a resistor 229, the central voltage divider 223, normally closed contacts 23| of a iirst relay 233 and normally closed contacts 235 of a second relay 231. This vcondition exists when the material 451:0 be welded has the maximum thickness. If material of thickness corresponding to the setting of the intermediate snap switch 11V is disposed between the electrodes 25 and 21, the intermediate switch snaps to its upper position 139-91, and a circuit is closed which extends from the upper terminal of the secondary I 99 through the exciting coil of the rst relay 2:33, the upper con tacts 81 of the switch 11, the lower contacts 89 of the central switch 19 to the intermediate tap |91 of the secondary. The first relay 233 picks up; its normally closed contacts 22| open, opening the shunt circuit through the central voltage divider 223, and its normally open contacts close, closing the shunt circuit through the lower voltage divider 225. Ii the material disposed be tween the electrodes has a thickness smaller' than that corresponding to the setting or the intermediate thickness switch 11, the switch 8| set for the thickest material snaps from the lower position 89-85 to the upper position 89h91. A circuit now closes through the exciting coil of the second relay 231, the switch contacts 91, to the intermediate tap |91 of the transformer. The normally open contacts 239 oi' the second relay 231 close, clos-ing a shunt circuit through the third voltage divider 221 and the normally closed conN tacts 235 of the second relay open, opening cirn cuits through the other Voltage dividers 223 and 225.

The third thyratron |81 is connected to time the so-called hold operation, that is, the time interval during which the welding electrodes 25 and 21 are held in engagement with. the material after termination of the ow of welding current. The anode |9| of the hold thyratron |81 is connected to the upper terminal of the secondary through the exciting coil 24| of the hold relay, normally closed contacts 243 of a relay 245 associated with the 01T thyratron |39 and one of the contacts 241 of a selector repeatnon repeat switch 249 which sets the system for repeat or non-repeat operation. In the system as shown in the drawing, the selector switch 249 is set for repeat operation. The grid |95 of the hold thyratron |81 is connected to the lower terminal of the secondary through a capacitor 25| through a resistor 253 and through normally closed contacts 255 of the weld relay. The capacitor is shunted by a voltage divider 251 as is the capacitor 203 of the squeeze thyratron.

The fourth thyratron |89 is connected to time the oii operation, that is, time interval during which the welding operation `is discontinued so that the material 45 may be reset. The anode |9| of the oil thyratron |89 is connected to the upper terminal of the secondary through the exciting coil of the off relay 245, normally closed contacts 26| of the squeeze relay and a contact 253 of the selector switch 249. The grid |95 of the thyratron |89 is connected to the lower terminal of the secondary through a capacitor 265, a resistor 281 and normally closed contacts 269 of the hold relay. The capacitor 265 is shunted by a Voltage divider 21| in the same manner as the squeeze capacitor 203.

The sys-tem is prepared for operation by energizing the supply busses 2| in the usual manner by the closure of a switch 213 or a circuit breaker. When this switch. is closed, heating current is transmitted through the heaters of the thyratron cathodes |61 and |93. A time delay relay 215 is energized and, after a predetermined time interval, operates closing contacts 211 in series with the exciting coil of the ring relay |19. 'lhis circuit is, however, open at several other points and ring does not occur. The time interval of the relay 215 is sufficient to permit the cathodes of the thyratrons to attain the proper temperature for emission.

The Welding operation may be initiated by closing a push button 219 or a foot switch. Current now flows through the coil of the solenoid relay 299 in a circuit extending from the upper terminal of the secondary through the push button 219, the coil of the solenoid relay, norm-ally closed contacts 28| of the hold relay to the intermediate tap |91- oi the secondary. The solenoid relay operates, closing a first set of normally open contacts 283. These contacts close a circuit through the Welder solenoid coil 285, actuating the welding electrodes 25 and 21 to apply pressure to the work. A second set of normally open contacts 283i of the solenoid relay in circuit with the coil or the ring relay |19 are now closed, but this closure has no immediate effect, as the circuit is elsewhere open. A third set of normally open contacts 299 of the solenoid relay are closed across the push button 219 and lock in the solenoid relay. The normally closed contacts 201 of the solenoid relay in circuit with the capacitor 293 associated with the squeeze thyratron |83 open. This capacitor 283 discharges gradually through its associated voltage divider 2|3 after a predetermined time interval equal to the desii-ed squeeze time the thyratron |83 becomes conductive.

Current now hows through the coil 20| ofthe squeeze relayin a circuit extending from the upper terminal of the secondary |99 through the coil, the thyratron |83 to the intermediate terminal oi the secondary. The squeeze relay operates, opening the two sets of normally closed contacts 22| and 29| and clos-ing its normally open contacts 29|. The rst set of now open con* tacts 29| opens a circuit through the exciting coil of the off relay 245 and prevents its operation until the welding cycle is completed. The now closed contacts 29| close a circuit through the exciting coil of the firing relay |19 which extends from the upper terminal of the secondary 99 through the now closed contacts 211 of the time delay relay 215, thenow closed contacts 29| of the squeeze relay, the exciting coil of the firing relay |19, the now closed contacts 281 of the solenoid relay 209, normally closed contacts 293 of the weld relay to the intermediate terminal |91 of the secondary. The firing relay operates, closing the contacts |8| in the output circuit of the phase shifter |15 and causing the ring thyratrons 9| and their corresponding ignitrons |59 to fire. Current is now conducted through the ignitrons and through the primary |1 of the weldtransformer. The resulting current induced `in the secondary I9 performs the Welding operation. The other now open contacts 22| of the squeeze relay break the charging circuit of the ,capacitor 2|1 Iassociated with the weld thyra# tron |85. The capacitor is gradually discharged through one or the other of the voltage dividers 223, 225, 221, depending on the setting of Athe snap switches 11, 19, 8| and the associated relays 233, 231. When the capacitor 2 |1 has discharged to predetermined potential, the weld thyratron 85 becomes conductive. The voltage divider 223, `225 or Y22"! shunting the capacitor 2H is so set as to correspond to the thickness of the material between the welding electrodes which has determined the setting of the snap switches 11, 19 or 8|. If all. three switches are in the down position, the time is short; if one of the switches 11 is in the up position, the time is longer; if two of the switches 11 and 119 are in the up position,

time is still longer. t When the weld thyratron I `85 becomes conductive, it causes the weld relay to operate. Opera- 75A tion of the latter results in the opening of its two setsjofnormally closed contacts 255 and 293. By opening of the latter set 293 of these contacts, the circuit through the exciting coil of the iiring relay |19 is opened, and the flow of welding current is interrupted. The opening of the other set 2 55 of these contacts results in the opening vof the ch-arging circuit ofthe capacitor 25| associated with the hold thyratron |81. This cal pacitor now gradually discharges through its associated voltage divider 251 and, after a preset hold interval, the hold thyratron |81 becomes conductive. l

When the hold thyratron conducts, it causes the hold relay to operate and to open its two sets of normally closed contacts 269 and 26|. The opening of the first set of contacts opens a circuit through the coil of the solenoid relay 29, causing the latter to drop out. The lower normally open contacts 283 of the solenoid relay 209 now open, opening the circuit through the solenoid 285 to permit removal of the welded materi-al. The second normally open contacts 281 of the solenoid relay provide a second open point in the circuit of the coil of the firing relay |19, thus permitting the normally closed contacts 293 of the weld relay to reclose when the weld thyratron |85 is subsequently rendered non-conductive. The normally closed contacts 201 and 289 of the solenoid relay 209 also reclose, the latter opening the lock-in circuit karound the push button 219 and the former permitting the capacitor 203 in the grid circuit of the squeeze thyratron |83 to rech-arge. The capacitor 203 recharges during the negative half periods of the potential supplied by the secondary and in a short time interval reaches a potential such that the squeeze thyratron |83 becomes non-conductive when its anode potential becomes negative, The squeeze relay 20| now drops out. Its upper normally closed contacts 26| reclose the circuit through the exciting coil of the off relay 245, its lower normally closed contacts 22| reclose the charging circuit for the capacitor 2|1 associated with the'weld thyratron |85. Its intermediate contacts 29| open a second point in the circuit of the exciting coil of the firing relay 219. By the closing of the lower contacts 22| of the squeeze relay 20|, the weld thyratron system is reset for operation.

l The opening of the other set of normally closed contacts 269 ofthe hold relay 24| opens the charging circuit of the capacitor 265 associated with the oir thyratron |89. This capacitor gradually discharges through its associated Voltage divider 21, and after a predetermined time interval, its potential reaches a magnitude at which the off thyratron |89 becomes conductive. The off relay 245 now operates and the opening of its normally closed contact 243 opens a circuit through the "hold thyratron |81 causing the latter to become deenergized and resetting the hold system. By the previous closure of normally closed contacts 255 of the weld relay 2|5 in its grid circuit, the grid circuit of the holdl nected to the junction of the normally open 12 locked-in contacts 289 of the solenoid relay 209 and the contacts of the push button 219. The off circuit is now disconnected from the system, andthe system must be reset manually by the operator.

Although I lhave shown and described certain specic embodiments of my invention, I am fully aware that many modiiications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. The method of weldingmetals of different thicknesses with apparatus `including welding electrodes, means for applying force between said metals of a given thickness and said electrodes and means for supplying current to weld said metals of a given thickness; which comprises the steps of applying a given force between said electrodes and said metals of one thickness, transmitting current ci a given peak magnitude through said metals of said one thickness, setting the time during which said current is transmitted in accordance with the thickness of said metals of said one thickness, applying substantially said given force between said electrodes and said metals of a diiierent thickness, transmitting current oi substantially said given peak magnitude through said metals of said diierent thickness, and setting the time during which said last-named current is transmitted in accordance with said diierent thickness.

2. The method of welding metals of different thicknesses, said metals having a range of thicknesses within which the thickness of the thickest metal does not exceed six times the thickness of the thinnest metal, with apparatus including welding electrodes, means for applying force between said metals of a given thickness and said electrodes, and means for supplying current to weld said metals ofv a given thickness; which comprises the steps of applying a given force between said electrodes and said metals of one thickness within said range, said force being `set at such magnitude as to produce a satisfactory weld for the thickest metal within said range, transmitting current of a given magnitude through said metals of said one thickness, setting the time during which said current is transmitted in accordance with said one thickness, applying substantially said given force between said electrodes and-said metals of another thickness within said range, transmitting vcurrent of substantially said given magnitude through said metals of'said other thickness, and setting the time during which said last-named current is transmitted in accordance with said other thickness.

3. The method of welding metals of different thicknesses, said metals having a range of thicknesses within which the thickness of the thickest metal does not exceed six times the thickness of the thinnest metals, with apparatus including welding electrodes, means for applying force between said metals cf a given thickness and said electrodes, and means for supplying current to weld said metals of a given thickness; which comprises the steps of applying force between said electrodes and said metals of a given thickness within said range, said force being set at such magnitude as to produce a satisfactory weld for the thickest of said metals within said range, transmitting current of a given peak magnitude through said metals of said one thickness, said current being set in accordance with said set force, setting the time during which said current is transmitted in accordance with said one thickness, applying said given force of substantially said magnitude between said electrodes and said metals of another thickness within said range, transmitting current ci substantially said peak magnitude through said metals of said other thickness, and setting the time during which said last-named current is transmitted in accordance with said other thickness.

4. The method of welding low carbon steel or different thicknesses, said steel having a range of thicknesses within which the thickness ci the thickest steel does not exceed six times the thickness of the thinnest steel, which apparatus including welding electrodes, means for applying force between said steel and said electrodes, and means for supplying current to weld said steel; which comprises the steps of applying a force of a predetermined magnitude between said electrodes and said steel of one thickness within said range, said predetermined magnitude being such as to produce a satisfactory weld for the thickest of said steel within said range, transu mitting current of a predetermined peak magnitude through said steel of said one thickness, said current being maintained within plus or minus ten per cent oi I in the equation in which F is said set force in pounds and I is the current in R.. M. S. amperes, setting the time during which said current is transmitted in accordance with the thickness oi the steel of said one thickness, applying said force F and said current I to steel of another thickness within said range and setting the time during which said current is transmitted in accordance with said other thickness.

5. The method of welding low carbon steel of different thicknesses with apparatus including welding electrodes, means for applying force between said steel and said electrodes, and means for supplying current to weld said steel; which comprises the steps of applying a force F in pounds between said electrodes and said steel of one thickness, which is of the order determined by the equation where t is the thickness in inches of the thickest steel to be welded, transmitting current of a predetermined peak magnitude through said steel of said one thickness, setting the time interval during which said current is transmitted in accordance with said one thickness, applying substantially said force F between said electrodes and said steel of another thickness, transmitting current of said predetermined magnitude through said steel of said other thickness and setting the time interval during which said last-named current is transmitted in accordance with said other thickness.

6. The method of welding low carbon steel of diierent thickness from a 60-cycle commercial alternating current source with apparatus including welding electrodes, means for applying force between said electrodes and said steel, said force F in pounds being independent of thickness and being determined from the equation in which t is the thickness in inches of the thick- 14 est steel to be welded, and the dat end diameter d in inches, the angle oi taper A in degrees, and the equivalent spherical radius R in inches of said electrodes being determined substantially by the equations and means for transmitting current through said electrodes and said steel, the R. M. S. magnitude 1 in amperes of said current being given by the equation and being within plus or minus ten per cent of I; which comprises the steps of applying substantially said force F between said electrodes and said steel of one thickness, transmitting current ci said R. M. S. magnitude I through said steel of said one thickness during a time interval equal to N cycles of said source, where in which t is said one thickness in inches, applying substantially said force F to steel of another thickness and transmitting current of substantially magnitude I through said steel of said other thickness for N1 cycles of said source Where where t1 is said other thickness in inches.

7. The method of resistance welding metals of different thickness over a predetermined range of thickness with a single pair of welding electrodes adapted for said range of thickness which engage said metals therebetween and through which welding current is supplied; which comprises setting the pressure between said electrodes and the average magnitude of said current each at a fixed value to correspond to the maximum thickness of said range; applying substantially said set pressure between said electrodes and said metals of one thickness within said range, transmitting current of said average magnitude through said metals of said one thickness for a time interval dependent on said one thickness, applying substantially said set pressure between said electrodes and said metals of another' thickness within said range, and transmitting current oi substantially said average magnitude through said last-named metals for another time interval dependent on said other thickness.

JULIUS HEUSCI-IKEL.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATESy PATENTS Number Name Date 1,744,804 Sanborn Jan. 28, 1930 1,959,690 Roth May 22, 1934 2,024,542 Simon Dec. 1'7, 1935 2,081,124 Vicario May 18, 1937 2,354,190 Benkert July 25, 1944 OTHER REFERENCES Welding Handbook, 1942, pages 270 and 271. American Welding Society, 33 West 39th Street, New York, N. Y. 

